The present invention is related to the field of DC—DC power converters.
Among the myriad types of circuit topologies employed in DC—DC power converters is a converter known as the “two-inductor boost converter”. This converter has a boost, or voltage-step-up, transfer function, and employs two parallel inductors with partially overlapped conduction. The two-inductor boost converter exhibits benefits particularly in high power applications due to the splitting of high input current between two inductors and the resulting reduction in I2R power loss in both copper windings and primary-side switches. An interleaving control strategy can be used to reduce input current ripple. Implementation of the topology can be in either non-isolated or isolated format. The isolated boost topology is attractive in applications such as isolated power factor correction (PFC) and in battery- or fuel-cell-powered devices to generate high output voltage from low input voltage.
One problem with the basic two-inductor boost converter topology is its limited power regulation range. Due to the nature of the control required for boost operation, the magnetizing currents of the two inductors cannot be limited, and thus a minimum output power level is required. If the load demands less power than this minimum level, the output voltage increases abnormally because excessive energy has been stored in the inductors.
U.S. Pat. No. 6,239,584 B1 of Jang et al. shows a solution to this limitation on minimum power. Referring for example to FIG. 2, an auxiliary transformer is inserted in series with the two inductors L1 and L2. The transformer magnetically couples the two input current paths, forcing the currents in the two inductors to be identical. Theoretically, the input current only increases when both of the switches S1 and S2 are on. If the overlapping between the two driving signals is small, the inductor currents become discontinuous. This improvement makes the two-inductor boost circuit attractive in application. However, a disadvantage of the approach is that the circuit requires four magnetic components on the primary side, thus requiring additional circuit board space.
It is generally known in the prior art to utilize so-called “integrated magnetics” circuit techniques to achieve certain efficiencies and/or operating characteristics, including reduced overall circuit size. Multiple windings are employed on a single flux-conducting core to implement multiple functions, in contrast to the traditional use of discrete inductors and transformers that are wired together to realize similar functions. It would be desirable to realize the benefits of integrated magnetics in two-inductor boost converters.